1. Field of the Invention
The present invention relates to systems and methods for manufacturing tab head assembly (THA) flex circuits. More specifically, the present invention relates to drive systems for linear bake ovens used in the fabrication of flex circuits.
2. Description of the Related Art
Flexible circuits, often referred to as `flex circuits`, are used in a number of applications. In an illustrative application, a flex circuit is used to convey electrical signals from a printer to an inkjet pen. The flex circuit used for this application is often fabricated on tab head assembly (THA) tape. THA tape is a strip of polyester or polyimid material such as a Mylar or Kapton which provides a substrate into which multiple copper conductors are embedded. The tape is typically on the order of 2 inches wide and 2 mils (0.002 inches) thick. A plurality of sprocket holes are provided along the edge of the tape on either side of a central die area onto which a silicon die is bonded with a suitable epoxy.
Electrical signals are communicated from the printer to the die through the copper circuitry in the Kapton material and into the silicon die. As described more fully in U.S. Pat. No. 5,568,171 issued Oct. 22, 1996 to Keefe et al., the specification and drawings of which are incorporated herein by reference, the electrical signals selectively activate a number of resistors in integrated circuit print heads fabricated in the die. The flow of current through the resistors heats and vaporizes ink and cause it to be expelled through a small nozzle toward print media, e.g., paper.
Fabrication of the THA involves pulling the tape off a reel with a linear drive system such as that manufactured and sold by Owens Design in Fremont, Calif. The drive system pulls the tape through a bake oven which cures the epoxy interface between the Kapton and the die. The conventional oven is actually eight ovens arranged in series to provide varying temperature environments for the tape as it moves therethrough: a gradually increasing thermal environment in a first few ovens, a stable temperature environment through the middle ovens, and a decreasing temperature environment through the last two or three ovens.
Current manufacturing techniques require a high tension (e.g. on the order of 1200 grams) on the tape throughout the curing process. The conventional linear drive system maintains high tension with supply and take-up sprocket wheels having a plurality of sprockets designed to engage sprocket holes on the THA tape. The high tension is maintained with a 90.degree. bend of the tape around the sprocket wheels.
Unfortunately, for current more demanding applications, the desired length of the rigid silicon die has grown to one inch. Accordingly THA tape carrying such dies can not be wrapped around a sprocket wheel under such high tension without an unacceptable amount of stress, deformation, and damage to the tape. Such damage to the THA tape has been found to include excessive wrinkling, delamination, broken TAB contacts, or sprocket hole damage.
Hence, there is a need in the art for a safe and effective system and method for fabricating THA tape for inkjet pens without exposing the tape and any long die thereon to undesirable stress, deformation, and damage.